Hi Everyone, Intel has a document called "Branch and Loop Reorganization to Prevent Mispredicts" (https://software.intel.com/en-us/articles/branch-and-loop-reorganization-to-prevent-mispredicts). In the document, they say to: if ( C ) // most common case ... else if ( A ) // 2nd most common case ... else if ( B ) // 3rd most common case ... They also say to: switch ( v ) { default: // most common case ... case S: // 2nd most common case ... case R: // 2nd most common case ... case T: // 2nd most common case ... } Above, (A,B,C) and (R,S,T) are ordered based on profiling data, so we know 'C' is most common in the first example, and 'default' is most common in the second example. My question is, does the same hold for GCC? Should the most likely statement appear first to provide a hint to the compiler? Related, we tried to provide the hints via __builtin_expect, but benchmarking showed the program mostly slowed down by a small amount rather than speed up. My apologies if this horse has been beat to death. I'm trying to find a canonical answer, but search is failing me. Cf., https://www.google.com/search?q=gcc+"branch+prediction"+order+of+statements+site%3Agcc.gnu.org Thanks in advance.
